نشریه روابط خاک و گیاه
پیاپی 56 (زمستان 1402)

Water contamination by heavy metals is an environmental threat, endangering human health. Phytoremediation, through artificial wetlands, emerges as an eco-friendly method for heavy metals decontamination. This study aimed to assess the efficiency of Phalaris arundinacea L. (canary seed plant) in removal of arsenic and manganese from a saturated sand culture under different hydraulic retention times (HRT). The research consisted of two distinct experiments utilizing a completely randomized factorial design, encompassing three factors: two bed lengths (BL) of 50 and 100 cm, four inflow concentrations (Ci) of heavy metals (arsenic at 0, 2, 4, and 6 mg/L, and manganese at 0, 10, 20, and 30 mg/L), and five HRT (3, 6, 9, 12 and 15 days), in three replications. Results revealed that the maximum arsenic absorption (Absmax) (5.88 mg/L) occurred at Ci of 6 mg/L, HRT of 6 days and BL of 50 cm. However, the manganese Absmax (29.25 mg/L) was observed at Ci of 30 mg/L, HRT of 9 days and BL of 50 cm. Phalaris bio-concentration factors (BCF) were 2.29 and 0.15 for arsenic and manganese, respectively, highlighting superior arsenic absorption by 15.26 times. The surface absorption values of arsenic and manganese in the sand bed (qeAs=0.005 mg/g and qeMn=0.004 mg/g) confirmed the insignificant effect of this process in this experiment. The average maximum removal efficiency (RE) for manganese (99.61 %) attained at Ci of 20 mg/L, BL of 100 cm, on the fifteenth day, however that of arsenic (98.11 %) reached at Ci of 6 mg/L, BL of 50 cm, on the sixth day. These findings underscore the Phalaris exceptional capacity to efficiently remove dissolved manganese and arsenic under saturated conditions in the sand culture.

Phytoremediation through constructed wetlands stands out as environmentally friendly method for eliminating heavy metals from aquatic environments (Priyanka et al., 2017). The removal efficiency (RE) in these systems highly depends on the culture media, dissolved oxygen (DO), type of flow, hydraulic retention time (HRT) and plant species (Roy et al., 2022). The time to reach maximum absorption (Absmax) and maximum RE are the two basic criteria in the evaluation of phytoremediation plans. In some cases, a heavy metal utilizes the same absorption mechanism as a vital plant element. Despite heavy metal toxicity, it gets absorbed in quantities exceeding the plant's tolerance level, ultimately leading to the demise of the plant. Conversely, a heavy metal may be on the list of essential plant nutrients, but when present in excessive concentrations in the root environment, it is regarded as a toxic element. The plant utilized in this study, Phalaris arundinacea L., is locally known as canary seed plant in some regions of Iran (Mehrnia and Jalili, 2022). This research aimed to assess the removal capabilities of Phalaris arundinacea L. in absorbing arsenic and manganese from saturated sand culture under different HRTs.

Our research consisted of two distinct experiments utilizing a completely randomized factorial design, encompassing three factors: two BLs (50 and 100 cm), four Ci (arsenic at 0, 2, 4 and 6 mg/L, and manganese at 0, 10, 20 and 30 mg/L), and five HRT (3, 6, 9, 12 and 15 days), in three replications. For this purpose, 240 PVC pots were filled with washed sand (< 2 mm). The number of 5 and 10 Phalaris seedlings were planted in 50 and 100 cm pots, respectively. The average concentrations of DO in the inflow and outflow solutions were 13.7 and 1.2 mg/L respectively. Dissolved manganese and arsenic were measured by atomic absorption and a hybrid method, respectively. The manganese and arsenic concentrations in plant tissues were measured using standard methods followed by ash dissolution. Factors related to each pot were analyzed by SAS 9.3 software. The means were compared by LSD test at 5% probability level. The MS Excel was used for drawing the graphs.

Based on the analysis of variance, all the main and interactive effects of the treatments on the manganese and arsenic retention were significant (p < 0.01). The results also revealed that the Absmax of arsenic (5.88 mg/L) occurred at Ci of 6 mg/L and HRT of 6 days. However, the Absmax of manganese (29.25 mg/L) observed at Ci of 30 mg/L and HRT of 9 days. The Phalaris’ BCF values for arsenic and manganese were 2.29 and 0.15, respectively, highlighting its 15.26-fold greater effectiveness in accumulating arsenic compared to manganese. The average maximum RE for manganese (99.61 %) was attained at Ci of 20 mg/L on the fifteenth day, however, that of arsenic (98.11 %) was reached at Ci of 6 mg/L on the sixth day. It seems, at the commencement of the experiment, with DO=13.7 mg/L, arsenate (As V) was the prevalent form of arsenic in the root environment. Given its structural resemblance to phosphate, it was largely taken up by Phalaris. However, as the experiment approached its end, with lower DO (2.1mg/L), the remaining arsenic, in the form of arsenite (As III), exerted persistent toxicity, leading to the gradual deterioration of the plants. Similarly, the process of manganese absorption exhibited a declining trend starting from the ninth day onward. This decrease was attributed to the significant reduction in DO, disrupting the biological processes within the plant. In the context of this research, the calculated BCF (2) for Phalaris in the treatments with the highest concentrations of arsenic and manganese were determined to be 2.29 and 0.15, respectively.

The results of this research underscore Phalaris arundinacea L. remarkable ability to accumulate arsenic in comparison to manganese by a factor of 15.26, in saturated sand culture. As a native species, Phalaris exhibits significant promise as a phytoremediation agent in addressing heavy metals contamination.

In order to investigate the effect of calcium-enriched sepiolite under stress conditions on the concentration of nutrients in cucumber, an experiment was conducted with two factors of stress (control, salinity stress: 70 mM sodium chloride, alkalinity stress: 70 mM sodium bicarbonate, and combined salinity and alkalinity stresses: 70 mM sodium chloride + 70 mM sodium bicarbonate) and the levels of sepiolite (0, 10 and 20% w/w) in a completely randomized design. The results showed that calcium-enriched sepiolite had favorable effects on the concentration of nutrients and the dry weights of plant root and shoot. For example, in non-stressed conditions, with the application of 10 %w/w sepiolite, in addition to a 94% increase in the dry weight of the shoot, the concentrations of Mg and Ca in the shoot increased by 15 and 45%, respectively. With the application of 20% w/w sepiolite, the dry weight of the shoot increased by 80% in the conditions of salinity stress. Additionally, this treatment resulted in significant increases in the concentration of Cu in the shoot, Ca in the root, Mg in the root and shoot, and Fe in the root, with increases of 89, 63, 230, 38, and 656%, respectively. Overall, the findings of this research showed that the use of sepiolite in stressful conditions can be beneficial in improving the concentration of nutrients, especially Fe, Mg and Ca, and reducing sodium accumulation in cucumber.

Previous studies have shown that salinity and alkalinity stresses caused a reduction in growth of plants (Roosta, 2011). Sepiolite mineral has been found in different regions of Iran and its agricultural and industrial uses have been started (Galan, 1996). Although some researches have been done on the environmental applications of this mineral as an adsorbent, there is very little information about the use of calcium-enriched sepiolite in the plant culture environment. Therefore, considering the role of salinity and alkalinity in reducing the production of products and the characteristics of sepiolite clay, this research was conducted to investigate the effect of calcium-enriched sepiolite as a soil conditioner to reduce the adverse effects of salinity and alkalinity stresses on cucumber.

The studied sepiolite was obtained from a mine in Fariman and after being grinding it was saturated with calcium chloride. This research was carried out in the greenhouse of Vali-e-Asr University of Rafsanjan as a hydroponic culture in a medium containing perlite and Ca-enriched sepiolite. The experiments included three levels of sepiolite (0, 10% and 20% w/w) and four levels of stress (no-stress conditions as control, salinity stress by 70 mM sodium chloride, alkalinity stress by 70 mM sodium bicarbonate, and combined salinity and alkalinity stresses by sodium chloride 70 mM and sodium bicarbonate 70 mM). The treatments were arranged in a factorial way in the form of a completely randomized design with three replications. At the end of experiment, the plants were completely removed from the pots and the aerial and root parts were separated, and after washing with distilled water, they were dried at 70 ºC for 48 hours and then powdered. The total concentrations of Ca, Mg, Na, Cl, Zn, Cu, Fe and Mn in plants shoot and root were determined according to standard methods.

The results showed that the use of Ca-enriched sepiolite reduced the adverse effects of stress on the concentration of nutrients. In non-stressed conditions, the concentrations of Mn and Mg in the root and shoot increased due to 10% sepiolite application. The concentration of Ca in the root and shoot increased in all sepiolite-treated pots, and Ca-enriched sepiolite decreased Na concentration in the root and shoot. Under salinity stress, the concentration of Cu in the shoot, Fe and Ca concentrations in the root and Mn concentration in the shoot and root increased, but the concentrations of Zn and Mn in the root and shoot decreased due to 20% sepiolite application. Under alkalinity stress, the concentration of Cu in the shoot, Mn and Ca concentrations in the root, and Mg and Fe concentrations in the root and shoot increased while the Na concentration in the root decreased. Under the combined salinity and alkalinity stresses, the concentrations of Cu and Mn in the shoot, and Fe and Mg concentrations in the shoot and root increased.

Based on the results of this research, calcium-enriched sepiolite had favorable effects on the concentration of nutrients such as calcium, magnesium, and iron in cucumber plants, and by removing sodium from the reach of the plant, it reduced the adverse effects of salinity and alkalinity stresses of the culture medium. Therefore, calcium-enriched sepiolite can be suggested as an amendment under salinity and alkalinity stress conditions.

This study with the aim of determining the effect of deficit irrigation and mulching on watermelon was conducted with a preliminary experiment in the form of split plots and a design of complete randomized blocks with three replications, in the Research and Education Center of Agriculture and Natural Resources in the south of Kerman province (Jiroft), in 2021‒2022. Drip irrigation as the main plot at three levels of 100, 70 and 50% of water requirement and mulching in three levels of crushed date palm leaf, black plastic and no mulch, as the sub-plot, were considered. As results demonstrate, the main and interaction effects of the treatments on stem length, leaf area, yield, water productivity, leaf relative water content, photosynthetic pigments, proline, total phenol, leaf superoxide dismutase enzyme and fruit length and width were significant. The main effects of irrigation and mulching on internode length, membrane stability index and vitamin C, and the main effect of the irrigation on the percentage of fruit dry matter, stem branches, and the main effect of mulching on fruit shape and soluble solids were significant. Fruit pH and total acidity, tasting and lycopene were not significantly affected by the treatments. The highest yield (60.1 ton/ha) was observed in the full irrigation and plastic mulch, and the highest water productivity (15.1 kg/m3) was recorded in the 70% irrigation and plastic mulch, but no significant difference with full irrigation and plastic and date palm leaves mulches. The findings showed that the effectiveness of plastic mulch on the watermelon growth and yield was higher with 100% and 70% irrigation compared to 50% irrigation. The date palm leaf mulch, despite being superior to the control in the full irrigation, had insignificant positive effects in deficit irrigation levels due to its high sodium content (1800 mg/kg).

Deficit irrigation has been mentioned as one of the effective techniques for increasing the water productivity of plants. Deficit irrigation of 50% caused a decrease in yield and water productivity of watermelon in Valencia region of Spain (Abdelkhalik et al., 2019). The role of mulching in compensating the negative effects of deficit irrigation has been confirmed in the literature (Diaz-Perez, 2023). This research aims at investigating the effects of deficit irrigation and mulching on the growth, yield and fruit quality of watermelon and the possibility of replacing plastic mulch with date palm leaf mulch.

Irrigation as the main plot at three levels of 100, 70 and 50% of water requirement and mulching at three levels of crushed date palm leaf, black plastic and no mulch, as the sub-plot, were considered. Crimson B 34 watermelon seeds produced by Seminis company, were planted on January 2021, in plots with the size of 13.5 × 7 m, on furrows and ridges planting system (the width of furrows and ridges were 0.5 and 4 meters, respectively). After planting, bow-shaped wires were put on the planting rows and a transparent plastic was placed as a tunnel on them.

Analysis of variance of the plant growth, yield, water productivity, and some physiological and biological traits displayed that the main and interaction effects of treatments were significant. Some traits such as pH, titratable acidity, fruit taste and shape were not affected by the treatments. The main and interaction effects of the treatments on stem length, leaf area, yield, water productivity, leaf relative water content, photosynthetic pigments, proline, total phenol, leaf superoxide dismutase enzyme and fruit length and width were significant. The main effects of irrigation and mulching on internode length, membrane stability index and vitamin C, and the main effect of the irrigation on the percentage of fruit dry matter, stem branches, and the main effect of mulching on fruit shape and soluble solids were significant. Fruit pH and total acidity, tasting and lycopene were not significantly affected by the treatments. The highest yield (60.1 ton/ha) was observed in the full irrigation and plastic mulch, and the highest water productivity (15.1 kg/m3) was recorded in the 70% irrigation and plastic mulch, but no significant difference with full irrigation and plastic and date palm leaves mulches was obtained. Reducing the irrigation water from 100 to 70 and to 50% of crop evapotranspiration or ETc (estimated by the FAO-Penman-Monteith method) in all three types of the mulch led to a significant decreasing in yield (Y), which was caused by the occurrence of water stress. The first reduction in water use (i.e., from 100 to 70%) increased the water productivity (WP) even though not significantly, but the second reduction in water use (i.e., from 70 to 50%) significantly led to a decrease in WP.

Overall, the 100%ETc treatment with black plastic mulch will probably have the best result in terms of watermelon yield unless water shortage, water price, and irrigation cost are noticeable compared to the crop price. In this case, 70%ETc irrigation with black plastic will be a priority in terms of WP. Of course, the cost of mulching and its possible environmental consequences should be considered.

A review of research on soil and plant interactions in rangeland and desert ecosystems shows that the number of soil samples are not determined on a scientific basis. The present study, with the aim of using effect size and power analysis to determine the number of soil samples in three plant types of Salsola spp. was conducted in three arid and semiarid regions of Shahriar, Zirkouh and Zabol. In addition, 15, 10, and 5 soil samples were collected for each plant type, respectively. Some soil properties, including electrical conductivity, sand content, organic matter content, calcium carbonate equivalent, and saturation percentage, were determined in the laboratory. The number of samples was estimated after the initial sampling based on the calculated effect size (f) and the power of 80 % and before the sampling based on the medium effect size (f = 0.25) and the power of 60 %. The results showed that the power analysis of the three studied sites was 88, 56, and 38 %, respectively. To determine the minimum number of soil samples required to achieve a power of 80 %, at least 20 soil samples are required for Zabol and Zirkouh, and at least 12 soil samples are required for Shahriar. If there is no previous information about the soil properties, more than 50 soil samples must be collected from each plant type for a statistical comparison of three plant types with a medium effect size, a power of 80 %, and a significant level of 0.05.

 In the field of vegetation studies, there are statistical and graphical methods to estimate the number of plots needed for sampling, and their application has been approved in numerous research studies. In a review of research on soil and plant interactions in rangeland and desert ecosystems, it seems that the number of soil samples are not determined based on a scientific basis. Either by autecology or synecology, soil samples were taken from different depths at the first and end points of each transect according to the soil depth by using the random-systematic method (i.e., a total of 6–8 soil samples). The sampling scheme captures all the decisions and information, such as the purpose of the sampling, financial constraints, sampling method, sample size, method(s) of statistical analysis, and accuracy of results (Arzani and Abedi, 2015). One of the most frequent problems in statistical analysis is determining the appropriate sample size (Rostampour and Eftekhari, 2023). The present study has the aim of using effect size and power analysis to determine the number of soil samples in three plant types in the halophyte-psammophyte ecosystem of the arid and semi-arid regions.

The present study was conducted on three plant types of Salsola spp. in three arid and desert areas of Shahriar, Zirkouh, and Zabol. At Shahriar, Zirkouh and Zabol sites, 15, 10, and 5 soil samples were collected for each plant type, respectively. Then, the soil samples were passed through a 2-mm sieve and some soil properties, including electrical conductivity, organic matter content, sand content, calcium carbonate equivalent and saturation percentage were measured in the laboratory. In general, for estimating the number of samples based on power analysis, there is a need for three factors: effect size, power, and significant levels. In the present study, two methods were used to determine the number of soil samples: 1) the estimation of the optimal sample number after the initial sampling based on the calculated effect size (f) and the power of 80 %, and 2) the minimum number of samples before sampling based on the medium effect size (f = 0.25) and power of 60 %.

The results showed that with an increase in the number of soil samples, the power analysis of the three studied sites was 38, 56, and 88 %, respectively. To determine the minimum number of soil samples required to achieve a power of 80 %, at least 20 soil samples are required for the Zabol and Zirkouh sites, and at least 12 soil samples are required for the Shahriar site. If the effect size is unknown due to the absence of data variance, the numbers of samples required for the sample sizes of small, medium, and large, and to reach a power of 60 % at the level of 0.05, are about 209, 35, and 14 samples, respectively. If there is no previous information about the soil properties, for a statistical comparison of three plant types with a medium effect size, a power of 80 %, and a significant level of 0.05, more than 50 soil samples must be collected from each plant type.

As per guideline, a power of 80 % is often considered an acceptable threshold, and studies with a power of less than 50 % should not be usually conducted. Accordingly, only the Shahriar site has a power above 60 %. Therefore, sampling from the Zirkouh and Zabol sites was not adequate for the statistical analysis. If there is no previous information about the soil properties, at least 50 soil samples should be collected from each plant type to compare the statistical significance of the three plant types with a medium effect size (F = 0.25) and a significant level of 0.05.

Drought is one of the most important abiotic stresses that affects the growth and production of crops. Therefore, the need to breed cultivars that have high compatibility and low water demand is strongly felt. This study was conducted to evaluate the effect of irrigation levels on cultivars and promising lines of cotton, to use the stress tolerance and susceptibility indices for identification and selection of drought tolerant genotypes, as well as to compare cotton promising lines (KD-92-11, KD-92-17 and KD-92-19) with control cultivars of Aria and Ghoze Ghermez (which are suitable for cotton growing areas in Khorasan and Isfahan provinces). For this purpose, an experiment was performed according to the split-plot design with three replications under four irrigation levels (normal, 25, 50 and 75% deficit irrigation compared with normal) in 2020 at Kashmar. The results showed that the irrigation level had a significant effect on all traits except for keel percentage and earliness. The trait of single boll weight decreased by 7, 24 and 32% at the irrigation levels of 25, 50 and 75%, respectively, compared to the normal regime. In the same conditions, the total yield also decreased by 3, 34 and 48%, respectively. There was a significant difference between genotypes in terms of all studied traits (except for keel percentage and earliness) and drought tolerance and susceptibility indices, which indicates high genetic diversity among the genotypes and can be effective in improving selection in the breeding programs. Mean comparison of traits in the four irrigation levels showed that with the reduction of irrigation levels from 25 to 75%, the average of all traits decreased and the greatest decrease was observed in the 75% moisture regime. In each of the four irrigation levels, control cultivars were superior to promising lines in terms of single boll weight, second harvest yield, and total yield. However, in terms of the traits of keel percentage, early maturity, number of vegetative and reproductive branches, and number of open bolls, the promising lines were superior to the control cultivars. In each of the three moisture stress regimes, the control cultivars of Ghoze Ghermez and Aria did not show any difference in stress tolerance, but compared to hybrids, the promising lines had between 5 and 25% more stress tolerance in terms of various traits.

Drought is one of the most important abiotic stresses that limit the growth and production of agricultural plants and affects all morphological, physiological, biochemical and metabolic aspects of plants (Blum, 2011). Changing the cultivation pattern and identifying heat and drought tolerant plant species and cultivars with high adaptability and low water requirements are among the main objectives of plant breeding in arid and semi-arid regions of the world. Cotton, as a strategic plant and the most important fiber plant, is one of the most important agricultural plants that provides the connection between the two sectors of agriculture and industry and plays a valuable role in the economy of some countries. It shows greater tolerance to abiotic stresses than other major crops. However, extreme environmental conditions such as drought are severe threats to the sustainability of cotton crops in dryland agriculture and affect the growth, productivity, and quality of cotton fibers (Barzali et al., 2016). This study was conducted to evaluate the effect of irrigation levels on cultivars and promising lines of cotton, to identify and select the drought-tolerant cultivars, and to compare the cotton lines with control cultivars.

In this study, three promising lines resulting from the crossing of Herbaceum and Arboreum species (KD-92-11, KD-92-17 and KD-92-19) along with two diploid control cultivars (Aria and Ghoze Ghermez) were cultivated according to the split-plot design with three replications at four irrigation levels (normal or control, 25, 50 and 75% deficit irrigation compared with normal) in 2020 at the field of the Research and Training Station of Agriculture and Natural Resources in Kashmar. Then, in order to select for drought tolerance, a set of morphological traits (height, number of vegetative and reproductive branches, number of opened and closed bolls, and crown diameter) and agricultural traits (single boll weight) along with yield, earliness and keel percentage were measured. Some drought tolerance and susceptibility indices were also calculated based on the yield of genotypes under normal and drought stress conditions.

Drought stress had a significant effect on all traits except for keel percentage and earliness. There was a significant difference between the studied genotypes in terms of all traits (except for keel percentage and earliness) and indices, which indicates high genetic diversity among the genotypes. The mean comparison showed that with the reduction of irrigation level from 25 to 75%, the average of all traits decreased, and the greatest decrease was observed in the 75% moisture regime. In all four moisture regimes, control cultivars were superior to the lines in terms of single boll weight, the yield of the first cut, the yield of the second cut, and total yield. However, in terms of the other traits, promising lines were superior to the control cultivars. In all three moisture stress regimes of 25, 50, and 75%, the control cultivars of Ghoze Ghermez and Aria did not show any difference in stress tolerance, but compared to the lines, they had more drought tolerance.

Based on the results of this study, there was high genetic diversity between the studied genotypes, which can be used in the breeding programs. Drought stress negatively affected all traits and reduced their diversity. Most significant decrease was observed in the 75% moisture regime. In all of the moisture environments, control cultivars were superior to promising cotton lines in terms of yield and single- boll weight. However, promising lines were superior to control cultivars regarding the remaining traits. Moreover, in all three moisture stress regimes, the control cultivars of Ghoze Ghermez and Aria did not show any difference in terms of stress tolerance, but compared to the promising lines (KD-92-11, KD-92-17, and KD-92-19), they showed more drought tolerance.

Drought is one of the most important abiotic stresses limiting the survival, growth, and production of plants in many regions of the world including Iran. Genetically, different species adopt different strategies to confront with drought. One of the mechanisms that plants have evolved to adapt to the environmental changes is stress memory. In this study, different genotypes of smooth bromegrass were evaluated to investigate the drought stress memory and drought stress tolerance based on a greenhouse pot experiment. Thirty three genotypes of smooth bromegrass were evaluated in three moisture environments: control (C), once drought-stressed (D2), and twice drought-stressed (D1D2) in a factorial arrangement according to the randomized complete blocks design with two replications. The dry matter yield decreased by 45 and 36% in the one-stress and two-stress treatments compared to the control, respectively. These results indicated the role of drought stress memory in modulating drought stress through the influence on forage dry yield and root dry weight. The root dry weight reduced in the once stress and twice stress conditions by 32 and 19%, respectively, compared to the control environment. This finding shows the significant effect of stress memory on the root growth. Based on the principal component analysis, superior genotypes were identified for future researches. Overall, the results suggested that smooth bromegrass is capable to activate some drought stress memory mechanisms related to morphological and root traits.

Smooth bromegrass is particularly adapted to areas with medium and low annual precipitations and has a high drought tolerance when compared with the other grasses. Drought is one of the most important environmental factors with adverse effects on plant growth and development and affects all morphological, physiological, biochemical and metabolic aspects of plants (Farooq et al., 2009). Therefore, it is necessary to identify drought-tolerant genotypes (Saeidnia et al., 2017b). The term stress memory was first proposed by Trewavas (2003), as the plant's ability to access past experiences to better respond to future stresses. In open-pollinated species that are difficult to develop inbred lines, such as smooth bromegrass, the main breeding method is to create synthetic varieties that are obtained through the crossing of suitable parents. Besides, half-sib matting is one of the most common methods for obtaining genetic information such as estimating the additive effects and dominance of genes (Nguyen and Sleper, 1983). Saidnia et al. (2017a) in a study on the genotypes of orchardgrass species found superior genotypes for hay production. They also examined the genetic parameters and heritability of dry matter yield and introduced the superior genotypes for the further researches. Hence, this study was designed to investigate stress memory and its effect on improving drought tolerance in a smooth bromegrass germplasm.

This research was carried out from February 2017 to June 2018 in the research greenhouse located at the Isfahan University of Technology as a pot experiment. A sandy loam soil with bulk density, field capacity, and wilting point of 1.57 g cm-3, and 12.5 and 7.4 %w/w, respectively, was used for filling the pots. The genetic materials included 33 genotypes of smooth bromegrass that were collected from different regions of the country and some foreign gene banks. The genotypes were investigated in three moisture environments including control (C), once drought-stressed (D2) and twice drought-stressed (D1D2) as a factorial experiment in the form of a randomized complete blocks design with two replications.

The analysis of variance showed that drought treatments had a significant effect on most of the traits. A significant difference was observed between the genotypes regarding the measured traits indicating high genetic diversity among the genotypes. The secondary drought stress significantly reduced most of the traits. The dry matter yield decreased by 45 and 36% in the once-stress and twice-stress treatments compared to the control, respectively. These results indicated the role of drought stress memory through the effect on dry yield of forage and root dry weight. Also, the root dry weight was reduced by 32 and 19% in the conditions of one stress and two stress compared to the control environment, respectively, which shows the significant effect of stress memory on the root system. Multivariate analysis showed that under the twice stress condition compared to the other two moisture environments, the relationships of the traits have undergone severe changes, which is a confirmation of the effect of initial stress and stress memory.

This research indicated a high genetic diversity among the smooth bromegrass genotypes in terms of stress memory responses, which can be used in the selection methods. For example, the means of dry matter yield and root dry weight decreased to a lesser extent when grown in the presence of twice drought stress, than once drought stress. This finding shows that the mechanisms of the stress memory related to morphological and root traits in this plant are activated by applying preliminary mild drought stress and help the plant to have a smaller decrease in growth. Based on the principal component analysis, superior genotypes were identified for future research. The results of this research can be used in breeding programs and future genetic research. It is also suggested that suitable genotypes be studied more in field conditions over several years.